1. Field of the Invention
The present invention relates to a light-emitting semiconductor device that emits blue light and uses a Group III nitride compound. Specifically, the invention relates to reducing the surface areas occupied by electrodes or bonding pads on a surface layer of the device to increase the quantity of light emitted from the device.
2. Description of the Prior Art
It has been known that an aluminum gallium indium nitride (AlGaInN) compound semiconductor may be used to obtain a light-emitting diode (LED) which emits blue light. This semiconductor device is useful because of its high luminous efficiency resulting from direct electron transition and because of its ability to emit blue light, which is one of the three primary colors.
Irradiating an electron beam into and heat treatment of a magnesium (Mg) doped i-layer alters it to exhibit p-type conduction. As a result, an LED with a double hereto p-n junction structure made of an aluminum gallium nitride (AlGaN) p-layer, a zinc (Zn) doped indium gallium nitride (InGaN) emission layer, and an AlGaN n-layer becomes useful instead of a conventional LED of metal insulator semiconductor (MIS) structure which includes an n-layer and a semi-insulating i-layer.
As an example, the conventional LED with a double hetero-junction structure has a sapphire substrate on which an AlN buffer layer, a Si-doped layer, a Si- and Zn-doped layer, and a Mg-doped layer are consecutively formed. Electron irradiation or heat treatment in an atmosphere of nitrogen gases is carried out to change the Mg-doped layer into a layer with p-type conduction.
The conventional LED requires a relatively large surface area for ball bonding-type connections between its bonding pads or electrodes and its bonding wire. As shown in FIG. 9 (a top view of the LED), a bonding pad or electrode 37 for a p-layer 36 and an another electrode 38 for an n-layer and an emission layer (not shown) are formed on the p-layer 36. Gold (Au) bonding wires 31 and 32, which are fabricated by a wire bonding method utilizing a conventional ball bonding tool, connect the electrodes 37 and 38 with their lead pins (not shown). This ball bonding tool requires electrodes with a relatively large surface area; the surface area occupied by the electrodes being opaque such that it impedes light emission from that light-emitting side of the device upon which the bonding pads or electrodes 37, 38 are situated. Consequently, the conventional LED results in poor luminous emission.